Device for detecting the position of at least one shaft which has a reference mark

ABSTRACT

A device for detecting the position of a shaft of an internal combustion engine is described, in which a sensor disc which is connected to the shaft and has at least one reference mark is sensed by at least one sensor and the output signals obtained are evaluated in the control device. So that the position of the shaft is known immediately after the internal combustion engine is started up, the last position to be determined after the internal combustion engine is switched off and after the shaft coasts to a standstill is stored in a non-volatile memory of the control device and, after the internal combustion engine is switched on again, is used to determine and output the first fuel injections during a starting phase. 
     In order to improve the accuracy, a detection of the direction of rotation is additionally carried out so that a correction can take place if the shaft turns backwards to a certain degree as a result of the engine swinging back.

PRIOR ART

The invention is based on a device for detecting the position of atleast one shaft which has a reference mark or at least one sensor disc,which has a reference mark and is connected to the shaft, of the generictype of the main claim and can be used in particular in conjunction withthe control of the fuel injection in internal combustion engines.

In a multi-cylinder internal combustion engine in which it can becalculated in a control device when and how much fuel per cylinder is tobe injected, it must be ensured that the fuel is fed to the individualcylinders at the correct time and in the correct quantity. So that thecalculations can be carried out correctly, the respective position ofthe crankshaft or camshaft of the internal combustion engine must beknown; it is therefore customary, and is described for example in EP-PS0 017 933, for the crankshaft and the camshaft to be each connected to adisc on whose surface at least one reference mark is provided, aplurality of marks of the same kind, also referred to as increments,usually being additionally provided on the crankshaft disc.

The two rotating discs are sensed by appropriate fixed sensors.Unambiguous information relating to the position of crankshaft andcamshaft can be acquired from the sequential timing of the pulsessupplied by the sensors, and corresponding drive signals for theignition system or fuel injection system can be calculated in thecontrol device.

The known system has the disadvantage that unambiguous positiondetection is only possible after a specific degree of rotation of thetwo shafts since, for this position detection, it is necessary to waituntil the reference marks pass by the respective sensors. So that acorrect fuel injection can take place directly after the internalcombustion engine starts, the exact position should, however, be knownimmediately after starting.

ADVANTAGES OF THE INVENTION

The device according to the invention having the characterizing featuresof Claim 1 has the advantage that the position of the camshaft orcrankshaft is known in the control device directly after the internalcombustion engine is switched on so that the said control device canbegin immediately to assign the injection to the cylindersappropriately.

This is made possible in that coasting detection takes place after theignition and fuel injection systems are switched off, the coastingdetection starting after the ignition lock is switched off. During theafter-running phase, the signals supplied by the sensors are stillevaluated by the control device. This evaluation does not end until thecrankshaft or camshaft has come to a standstill.

The detection of the angular positions of the two shafts when at astandstill which is thus possible is stored in a non-volatile memory inthe control device and used for the calculations of the start ofinjection when the engine is restarted.

Further advantageous embodiments of the invention are disclosed in thesubclaims. Here, it is advantageous that when the position of the shaftis determined when it is at a standstill, the data determined during thenormal operation of the internal combustion engine are included in thecalculations.

It is particularly advantageous that, after restarting, correctionvariables can be determined with the aid of the determined shut-offposition and the crankshaft position found during the synchronization,with which correction variables the swinging back of the internalcombustion engine can be compensated and, at the same time, thesecorrection variables are preferably adaptable in a cylinder-selectivefashion.

DRAWING

The invention is illustrated in the drawing and explained in greaterdetail in the subsequent description.

FIG. 1 shows a rough overview of the arrangement of crankshaft andcamshaft together with the associated sensors and the control device inwhich the calculations take place.

In FIG. 2 there is a flow diagram which shows the sequence according tothe invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

In FIG. 1, the components of an internal combustion engine which arerequired for the explanation of the invention are illustrated by way ofexample. Here, a sensor disc is designated by 10, which disc isconnected rigidly to the crankshaft 11 of an internal combustion engineand has on its circumference a plurality of angular marks 12 of the samekind. In addition to these angular marks 12 of the same kind, areference mark 13 is provided which is realized for example by means ofthe absence of two angular marks.

A second sensor disc 14 is connected to the camshaft 15 of the internalcombustion engine and has on its circumference a segment 16 with whichthe phase position of the reference mark on the crankshaft disc isdetermined. 17 indicates the connection present between crankshaft andcamshaft, the said connection rotating the camshaft at half the rpm ofthe crankshaft.

The illustrated shape of the sensor discs connected to the crankshaft orcamshaft is exemplary and other shapes can be chosen to replace it.

The two sensor discs 10, 14 are sensed by sensors 18, 19, for exampleinductive sensors or Hall sensors, and the signals which are produced inthe sensors as the angular marks pass by are fed to a control device 20and prepared there in a suitable manner, for example each edge of a markproducing a pulse. These pulses and their sequential timing are furtherprocessed in the control device 20.

The control device 20 receives via various inputs further inputvariables which are required for the open-loop or closed-loop control ofthe internal combustion engine, which variables can be measured byvarious sensors. The following are examples of such sensors: atemperature sensor 21 which measures the engine temperature, a throttlevalve sensor 22 which records the position of the throttle valve, apressure sensor 23 which measures the pressure in the intake manifold orthe pressure in a cylinder of the internal combustion engine.Furthermore, via the input 24 an "ignition on" signal is fed which issupplied by the terminal KL15 of the ignition lock when the ignitionswitch 25 is closed .

On the output side, the control device which comprises a computing orstorage means (not illustrated) and a permanent memory, designated by30, provides signals for the ignition and fuel injection for appropriatecomponents (not designated in greater detail) of the internal combustionengine. These signals are output via the outputs 26 and 27 of thecontrol device 20.

Depending on requirements, further sensors can be used whose signals arefed to the control device; the control device 20 can also output furthersignals required for the closed-loop control of the internal combustionengine. It is not necessary either for all the illustrated sensors to bepresent.

The voltage is supplied to the control device 20 in a customary mannerwith the aid of a battery 28 which is connected to the control device 20via a switch 29 whilst the internal combustion engine is operating andduring an after-running phase after the engine is switched off.

With the device described in FIG. 1, the position of the two shafts 11,15 can be detected at any time during the operation of the internalcombustion engine. Since the assignment between crankshaft and camshaftis also known, as is the assignment between the position of the camshaftand the position of the individual cylinders, after the detection of thereference mark a synchronization can take place and after asynchronization has taken place the fuel injection and the ignition canbe open-loop or closed-loop controlled in a known manner. Such controlof an internal combustion engine is described for example in the GermanOffenlegungsschrift DE-A 39 23 478 and for this reason is not explainedin greater detail here.

However, with the device described in FIG. 1 detection of the engineposition according to the invention is also possible in the coastingmode during the so-called after-running phase. This after-running phase,which follows the customary normal operation of the internal combustionengine which is known for example from the abovementionedOffenlegungsschrift, will be explained with reference to the flowdiagram according to FIG. 2.

In the control device 20, it is tested in step S1 whether a switch-offdesire of the driver is present. This detection takes place byevaluating the "ignition on" signal supplied via input 24. If there isno switch-off desire, the normal operation of the internal combustionengine continues (step S2). If, on the other hand, a switch-off desireis detected, the ignition and fuel injection are switched off by thecontrol device and the after-running phase is processed in step S3.

After the switching off of the ignition and of the fuel injection, theinternal combustion engine or the motor coasts to a stop. The controldevice 20 is still active during an after-running phase. Within thisafter-running phase which is longer than the coasting phase of theengine, signals which are supplied by the sensors 18 and 19 areevaluated. Therefore, it is possible to count out the pulses caused bythe marks 12 during the coasting phase.

Since the reference mark 13 of the sensor disc 10 is detected in eachcase by for example time intervals being evaluated between individualpulses, by counting out the pulses caused by the individual marks 12 therespective angular distance from the reference mark 13 can be determinedso that the exact position of the disc 10, and thus of the shaft 11, isalways known. The phase position is determined by comparing thecrankshaft reference and camshaft signal.

It is thus also possible to determine the exact position of the shaft 11and 15 when the shafts are at a standstill, and to store this positionin a non-volatile memory 30 in the control device. The detection thatthe shaft is at a standstill is designated by step S4 and the storage inthe non-volatile memory 30 of the position detected when the engine isat a standstill takes place in step S5.

After the after-running phase has expired, the control device isswitched off in step S6, and it remains in the switched-off state untilthe engine is to be restarted. When restarting takes place, thisrestarting is detected by the control device again with the aid of the"ignition on" signal and access is immediately made to the information,stored in the non-volatile memory 30, relating to the position of theshaft 11 or 15.

In an internal combustion engine, after the normal operation in whichthe position of the crankshaft and of the camshaft as well as theirsynchronization are known, and a cylinder detection has taken place, anunambiguous determination of the position of the crankshaft and of thecamshaft when at a standstill can take place by means of the evaluationof the signals of the sensors up until the engine comes to a standstilland the entire information can be stored in a non-volatile memory.

When the internal combustion engine is restarted, immediately after thestart signal is detected in step S7, in step S8 the injection times andthe start of the injection are calculated in relation to the angularposition with reference to these stored data which indicate the positionof the machine, and the injection for the next cylinder which can stillbe reached is output even before a renewed synchronization is present.

In step S9, a resynchronization takes place from the newly detectedposition of the crankshaft reference mark and camshaft reference mark,and the system goes over again to the normal calculation of the start ofinjection and the first ignition pulses are output by the controldevice.

The start and duration of injection during the entire start phase(before and after resynchronization) can be applied by means of variousdata.

In a further improvement, the direction of rotation of the engine isdetected from the sequential timing of the individual pulses supplied bythe sensors 18, 19 so that in the event of possible swinging back of theengine before it comes to a standstill the limit position can beappropriately corrected.

In addition, with the aid of the determined shut-off position and thecrankshaft position actually found during synchronization it is possibleto determine, after restarting, correction variables with which theerror caused by the swinging back of the engine can be partiallycompensated. These correction variables can be adapted in acylinder-selective fashion and can be included in the calculationsoccurring whenever restarting takes place.

If it is possible to detect the direction of rotation, an exact engineposition can be determined continuously by counting out in theafter-running phase the pulses supplied by the individual angular marks12 so that the stored engine position is also exact and when restartingoccurs the correct position is immediately available so that optimuminjection can take place.

It is thus possible for the injection to be started in correct phase asearly as the actuation of the starter so that all the cylinders can beappropriately supplied with fuel directly after switching on.

However if it is not possible to detect the direction of rotation, forexample as a result of a fault, or if the engine stalls during switchingoff, that is to say the engine is switched off without an "ignitionon/off" signal being supplied, the injection carried out during thestart phase is not carried out with the aid of the stored position databut rather the system waits until a synchronization has taken place. Thedetection of such states takes place by means of plausibility tests.

We claim:
 1. A fuel injection system for an internal combustion enginecomprising: a shaft position sensor arranged to detect a referenceindicator on said shaft and produce a corresponding sensor output signalrepresentative of a rotational position of said shaft; a microprocessorresponsive to said shaft position sensor output signal designed toprovide control of one of ignition and fuel injection for said internalcombustion engine; said microprocessor being programmed to evaluate saidsensor output signal also during a phase after an ignition is switchedoff until said shaft rotation ceases; said microprocessor furtherincluding a non-volatile memory and functioning to store a detectedshaft position signal at the instant of the cessation of shaft rotationin said non-volatile memory, providing a shaft "standstill position"signal to said non-volatile memory; said microprocessor furtherfunctioning to include said shaft "standstill position" signal data inthe control calculations for one of the injection and ignition uponrestart of said internal combustion engine.
 2. A device as defined inclaim 1, wherein said microprocessor is formed as a control device.
 3. Adevice as defined in claim 1, wherein said shaft is a crankshaft of theinternal combustion engine, said sensor being assigned to thecrankshaft.
 4. A device as defined in claim 1, wherein said shaft is acamshaft of the internal combustion engine, said sensor being assignedto the camshaft.
 5. A device as defined in claim 1; and furtherincluding another shaft position sensor, a crankshaft disc provided witha plurality of marks and at least one reference mark and mounted on acrankshaft so that said first mentioned sensor senses said crankshaftdisc, and a camshaft disc having at least one mark and mounted on acamshaft so that said camshaft disc is sensed by the other sensor and aphase position is determined by means of a defined position of said markon said camshaft disc with respect to said reference mark on saidcrankshaft disc.
 6. A device as defined in claim 1; and furtherincluding another shaft position sensor, a crankshaft disc provided witha plurality of marks and at least one reference mark and mounted on acrankshaft so that said first mentioned sensor senses said crankshaftdisc, and a camshaft disc having a plurality of marks matched to anumber of cylinders and mounted on a camshaft so that said camshaft discis senses by the other sensor and a phase position is determined bymeans of a sequence of said marks on said camshaft disc.
 7. A device asdefined in claim 1; and further comprising a crankshaft disc mounted ona crankshaft and provided with a reference mark to be sensed by saidsensor, said microprocessor being formed so that in order to determineexactly a position of the crankshaft a number of increments after theoccurrence of said reference mark is counted.
 8. A device as defined inclaim 1; and further comprising another shaft position sensor, and acamshaft disc provided with a segment to be sensed by the other sensorfor determining a phase position of said reference mark of saidcrankshaft disc, said microprocessor being formed so that in order todetermine exactly a position of the camshaft the number of increments iscounted in relation to a phase position.
 9. A device as defined in claim1; and further comprising a disc mounted on said shaft and having areference mark, said microprocessor being formed so that when theinternal combustion engine is switched on again after a detection ofsaid reference mark of the shaft, a synchronization is carried out andsaid microprocessor goes over to normal determination of an injectionangular position.
 10. A device as defined in claim 1, wherein saidmicroprocessor is formed so that a detection of a direction of rotationof the shaft takes place.
 11. A device as defined in claim 1, whereinsaid control device is formed is so that a correction of a shut-offposition takes place if the internal combustion engine turns backwardsand the correction takes place by counting out increments during areverse travel.
 12. A device as defined in claim 1, wherein said controldevice is formed so that a correction of a shut-off position takes placeif the internal combustion engine turns backwards, the correction takingplace by comparing a determined shut-off position and a shaft positionfound during a synchronization.
 13. A device as defined in claim 1,wherein said microprocessor is formed so that adaptable correctionvaluables are formed and an adaptation takes place in acylinder-selective fashion.
 14. A method of controlling fuel injectionin an internal combustion engine, comprising the steps of detecting areference indicator on said shaft by a shaft position sensor andproducing a corresponding sensor output signal representative of arotational position of said shaft; providing control of one of ignitionand fuel injection for said internal combustion engine by amicroprocessor responsive to said shaft position sensor output signal;programming said microprocessor to evaluate said sensor output signalalso during a phase after an ignition is switched off until said shaftrotation ceases; storing a detected shaft position signal at the instantof the cessation of shaft rotation in a non-volatile memory provided insaid microprocessor, and providing a shaft "standstill position" signalto said non-volatile memory; functioning said microprocessor further toinclude said shaft "standstill position" signal data in the controlcalculations for one of the injection and the ignition upon restart ofsaid internal combustion engine.
 15. A method as defined in claim 14;and further comprising the step of using a crankshaft as said shaft andassigning said sensor to the crankshaft.
 16. A method as defined inclaim 14; and further comprising the step of using a camshaft as saidshaft and assigning said sensor to the camshaft.
 17. A method as definedin claim 14; and further comprising the steps of providing another shaftposition sensor; providing the crankshaft and the camshaft of aninternal combustion engine with a crankshaft disc and a camshaft disccorrespondingly; arranging a plurality of marks and at least onereference mark on the crankshaft disc to be sensed by said firstmentioned sensor and arranging one mark on the camshaft disc to besensed by,the other sensor; and determining a phase position by means ofa defined position of said mark on the camshaft disc with respect tosaid reference mark on said crankshaft disc.
 18. A method as defined inclaim 14; and further comprising the steps of providing another shaftposition sensor; providing a crankshaft and a camshaft of the internalcombustion engine with a crankshaft disc and a camshaft disccorrespondingly; arranging a plurality of marks and said at least onereference mark on the crankshaft disc to be sensed by said firstmentioned sensor and arranging a plurality of marks matched to a numberof cylinders on the camshaft disc to be sensed by the other sensor; anddetermining a phase position by means of a sequence of the marks on saidcamshaft disc.
 19. A method as defined in claim 14, wherein the shaft isa crankshaft; and further comprising the steps of providing on saidcrankshaft a crankshaft having a reference mark; and determining exactlya position of said crankshaft by counting a number of increments afterthe occurrence of said reference mark.
 20. A method as defined in claim14, wherein the shaft is a camshaft; and further comprising the steps ofproviding another shaft position sensor; providing on said camshaft acamshaft disc with a segment to be sensed by the other sensor fordetermining a phase position of said reference mark on said crankshaftdisc; and determining exactly a position of the camshaft by counting outa number of increments in relation to a phase position.
 21. A method asdefined in claim 14; and further comprising the step of carrying out asynchronization when the engine is switched on after a detection of areference mark on the shaft, and then transferring the device to normaldetermination of an injection angular position.
 22. A method as definedin claim 14; and further comprising the step of providing a detection ofa direction of rotation.
 23. A method as defined in claim 14; andfurther comprising the step of providing a correction of a shut-offposition if the internal combustion engine turns backwards, by countingout increments during a reverse travel.
 24. A method as defined in claim14; and further comprising the step of providing a correction of ashut-off position if the internal combustion engine turns backwards, bycomparing a determined shut-off position and a crankshaft position foundduring a synchronization.
 25. A method as defined in claim 24; andfurther comprising the step of forming adaptable correction variables;and performing an adaptation in a cylinder-selective fashion.